Contents

History

The spiral model was defined by Barry Boehm in his 1988 article "A Spiral
Model of Software Development and Enhancement"[1]. This
model was not the first model to discuss iterative development, but it was the first
model to explain why the iteration matters.

As originally envisioned, the iterations were typically 6 months
to 2 years long. Each phase starts with a design goal and ends with the client (who may be internal) reviewing the
progress thus far. Analysis and engineering efforts are applied at each
phase of the project, with an eye toward the end goal of the
project.

Steps

The steps in the spiral model iteration can be generalized as
follows:

The new system requirements are defined in
as much detail as possible. This usually involves interviewing a
number of users representing all the external or internal users and
other aspects of the existing system.

A preliminary design is created for the new system.This phase
is the most important part of "Spiral Model". In this phase all
possible (and available) alternatives, which can help in developing
a cost effective project are analyzed and strategies are decided to
use them. This phase has been added specially in order to identify
and resolve all the possible risks in the project development. If
risks indicate any kind of uncertainty in requirements, prototyping
may be used to proceed with the available data and find out
possible solution in order to deal with the potential changes in
the requirements.

A first prototype of
the new system is constructed from the preliminary design. This is
usually a scaled-down system, and represents an approximation of
the characteristics of the final product.

A second prototype is evolved by a fourfold procedure:

evaluating the first prototype in terms of its strengths,
weaknesses, and risks;

defining the requirements of the second prototype;

planning and designing the second prototype;

constructing and testing the second prototype.

Applications

Game development is a main area where the spiral model is used
and needed, that is because of the size and the constantly shifting
goals of those large projects.[2]

The spiral model is mostly used in large projects. For smaller
projects, the concept of agile software development
is becoming a viable alternative. The US military has adopted
the spiral model for its Future Combat Systems program.
The FCS project was canceled after six years (2003 - 2009), it had
a 2 year iteration (spiral). FCS should have resulted in 3
consecutive prototypes (one prototype per spiral - every 2 years).
It was canceled in May, 2009